In the course of processing molten metals it is sometimes beneficial to treat the molten metal with gas. For example, gases such as nitrogen and argon are introduced into molten aluminum and alloys thereof to remove undesirable constituents such as hydrogen gas and non-metallic inclusions. Chlorine gas is introduced into molten aluminum and alloys thereof to remove alkali metals, such as magnesium. The gases added to the molten metal can chemically react with the undesired constituents to convert them to a form (such as a precipitate or a dross) that separates or can be separated from the molten metal.
As disclosed in U.S. Pat. Nos. 6,689,310 and 4,954,167 the gas can be dispersed in the molten metal using a device that includes a refractory shaft having a passageway through it connected to a rotor or impeller at its lower end. The gas travels through one or more openings of the rotor. The rotor can be configured to improve the distribution of the gas such as by more finely dividing gas bubbles. A motor rotates the refractory shaft. A gas source introduces gas into the refractory shaft.
U.S. Pat. No. 6,589,313 discloses a hollow shaft on the end of which is an impeller. The shaft and impeller are rotated and positioned at an angle relative to the bath by a complex apparatus. Solid flux and gas are added to the rotating shaft and dispersed in the molten metal.